Single turn trip coil having novel core and armature configurations



J. H. LEONARD 3,201,539 SINGLE TURN TRIP COIL HAVING NOVEL CORE AND ARMATURE CONFIGURATIONS Filed Jan. 25, 1963 2 Sheets-Sheet l M/ 54 m1 m8 m/ INVENTbR. {02 ml N 54A Am? JAMES LE0/V/M0 BY 0 7 ml .EE. 5. /0/

Aug. 17, 1965 J. H. LEONARD 3,201,539 SINGLE TURN TRIP COIL HAVING NOVEL CORE AND ARMATURE CONFIGURATIONS Filed Jan. 25, 1963 2 Sheets-Sheet 2 United States Patent Office 3,201,539 SINGLE TURN TRIP COIL HAVING NOVEL CORE AND ARMATURE CONFIGURATIONS James H. Leonard, Cedar Rapids, Iowa, assignor to I-T-E Circuit Ereaker Company, Phiiadelphia, Pa., :1 corporation of Pennsylvania Filed Jan. 23, 1963, Ser. No. 253,432 13 Claims. (Cl. 200-87) This invention relates to circuit interrupters in general and more particularly to a novel magnetic trip means operable at low current magnitude.

Molded case circuit breakers of low current rating, say in the range between and amperes, present certain problems when it is desired to incorporate therein a magnetic trip means which operates at relatively low current magnitudes. The obvious solution is to provide a multituru energizing coil for the magnet. However, because of crowded conditions in the circuit interrupter housing it is desirable to utilize a single turn for energization of the magnet. Further, the utilization of a single energizing turn rather than a multi-turn coil is more desirable in that the former is less expensive to construct and less expensive to assemble.

However, in low current rated circuit interrupters the magnetic trip means must act to move a cradle restraining latch through a distance sufiicient to unlatch the cradle. Because of this the air gap betwen the armature and magnet must be of a minimum dimension thereby imposing ditficult operating conditions upon the magnetic trip means. The instant invention provides a simple inexpensive solution to the problems previously outlined by providing what will be termed a dual characteristic magnetic means. That is, there is provided a U-shaped magnet with pole faces at the forward ends of the arms thereof. The armature is pivoted at one of its ends about an axis extending between the U-arms and located at one side of the magnet. Each of the U-arms is provided with an extension projecting forwardly toward the armature at the end thereof remote from the pivot.

The pivot end of the armature is of a width suificient to span the distance across the U-arms while the end of the armature remote from the pivot is of a width reduced sufiiciently so that this end of the armature will fit between the U-arms.

With the trip means in latching position the reduced width portion of the armature is disposed forward of the -arm extensions. Upon the occurrence of overload conditions the armature is attracted to the magnet thereby releasing .the cradle. In the attracted position the portion of the armature adjacent to the pivot engages the pole faces while the reduced width portion of the armature at the end thereof remote from the pivot is positionedbetween the U-arms.

It has been found that When this arrangement is compared a conventional U-shaped magnet where both annatures have the same distance of travel the magnetic force attracting the armature of the instant invention is the greatest magnitude in excess of the magnetic force attracting the conventional armature when the armature of the instant invention just reaches the entrance formed by the forward extensions of the U-arms. In addition, attracting forces at all distances from pick-up to this point are greater for a device constructed in accordance with the instant invention than for a prior art device.

I Accordingly, a primary object of this invention is to provide a novel construction for a magnetic trip means which is economical to produce andwill develop tripping forces at low current magnitudes.

Another object is to provide a novel magnetic trip means which forms a compact structure.

3,201,539 Patented Aug. 17,. 1965.

Still another object is to provide a novel magnetic trip having dual characteristics.

A still further object is to provide a magnetic trip means in which there is a U-shaped magnet having pole faces with forward extensions and a pivoted armature whose end remote from its pivot is of reduced width to fit between the extensions and whose end adjacent to the pivot is wider than the distance betwen the U-arms.

These as well as further objects of this invention shall become readily apparent after reading the following description of the accompanying drawings in which:

FIGURE 1 is a side elevation, with the housing cover removed, of a circuit interrupter which includes the dual characteristic magnetic trip means of the instant invention.

FIGURE 2 is an exploded perspective illustrating the relationship between most of the current carrying elements and the contact operating elements of the circuit interrupter illustrated in FIGURE 1.

FIGURES 3 through 5 are enlarged side elevations illustrating various positions for the magnet and armature constituting the magnetic trip means of the circuit interrupter illustrated in FIGURE 1. In FIGURE 3 the armature is in fully open or latching position; in FIG- URE 4 the armature is partially closed; and in FIGURE 5 the armature is in fully closed or trip position.

FIGURES 6 and 7 are front and end views of the elements illustrated in FIGURE 5 looking in the directions of arrows 66 and 7-7, respectively, of FIGURE 5.

Now referring to the figures. The construction and operation of substantially the entire circuit interrupter illustrated in FIGURES 1 and 2 is set forth in detail in my copending application, Serial No. 11,768, filed February 29, 1960, now Patent No. 3,152,232.

Circuit breaker 2i) includes a housing consisting of case 21 and a cover (not shown) secured to one another by rivets 23a. comprises line terminal 24, conducting strap 25, stationary contact 26, movable contact 27, contact arm 28, pressure point 29 at the upper end of contact arm 28, releasable cradle 30, bimetal 31, conducting braid 32, and load terminal contact member 33.

Spring 7? acts as a gripping means for a load conductor (not shown) which passes through case opening 78 into engagement with load contact 33. Adapter 77 is utilized to electrically connect line terminal 24 to a panel board has bar (not shown).

Extension 35, of operating member 34, projecting upwardly through opening 36 in the top of housing 21 constitutes a manual operating handle. Operating member 34 is also provided with an arcuate portion 37 extending in the direction of movement of handle 35 and disposed within arcuate groove 38 of case 21 and a similar groove in the case cover. The upper end of handle arm 39 extends into suitable recesses of operating member 34 while the lower end of arm 3 abuts a rounded internal formation of case 21 to form a pivot 40 for operating member 34 Main operating spring 41 is secured at one end 42 thereof to arm 39 where its bifurcated upper end engages member 34 while the other end 43 of spring 41 is connected to movable contact arm 28. Spring 41 is an open loop shaped tension member which urges the upper end of contact arm 28 to abut cradle 30 at joint 29. With cradle 30 in the latched position of FIGURE 1 circuit breaker 20 may be manually operated between its ON and OFF positions wherein contact 27 is respectively in and out of engagement with contact 26.

Cradle 30 is a generally V-shaped member having an opening 44 which receives case embossment 45 serving as a pivot for cradle 30 and the elements mounted thereto. Bimetal 31 is fixedly secured at one end 46 thereof to cradle 30 in the region of aperture 44. Latch mem- The current path through circuit breaker 20' her as is pivotally secured by rivet 49 and retainer spring 89 to cradle 30 at the free end portion 30a of cradle leg h. The free end portion 30a as well as tab '70 are embossed formations offset from the general plane of cradle 36. In forming portion 323 stop formation '71 is also formed. Stop 71 cooperates with notch 72. in latch member 48 to limit movement of latch 43 about its pivot '49.

Tab/70 is raised above one surface of cradle 3% while disk '73 is welded to the other surface of cradle 30. Tab '70 and disk 73 are operatively positioned and spaced from one another to form a pocket which receives the upper end of contact arm 28 in the region of joint 29 to provide guidance for arm 28 as contact 27 is moved into and out of engagement with contact 26. i

In the position of FIGURE 1 cradle 39 and the elements carried thereby are restrained against movement in a counterclockwise direction about pivot 45 to unlatched position through the engagement of intermediate latch member 48 with main latch member 51. Main latch member 51 is constructed of spring material and includes a portion of reduced area which fits over the back of magnet 52. Magnet 52 is of generally U-shaped cross-section (as will be described in detail) with braid 32 passing between the arms of the U to form the single energizing turn for magnet 52.

Armature 54 is pivoted at one of its ends about a pivotal axis 53 extending transverse to the U-arms of the magnet. The pivot is further defined by the right angle bend of main latch member 51, with the armature 54 being secured to main latch member 51 by rivet 55. The biasing action of the spring material forming main latch member 51 urges armature 54 in a clockwise direction about its pivot 53such that its opposite end is urged forward away from magnet 52. The lower end of armature 54 abuts case formation 56 to establish the air gap between the armature 54 and magnet 52 and also to establish the latch position for mem-,

ber 51.

Magnetic tripping occurs when with current exceeding apredetermined magnitude flows through braid 32 causing magnet 52 to generate flux attracting armature 54 with sufficient force to move it counterclockwise with respect to FIGURE 1 about pivot 53. This moves latch portion 51a of main latch member 51 to the right with respect to FIGURE 1 so that cradle 3% is no longer restrained. Thus, cradle Zitl under the influence of spring 41 rotates in a counter-clockwise direction about pivot 45 to trip position. When pivot 29 moves to the left of the line of action of spring 41 in its position of FIG- URE 1, spring 41 will urge contact arm 28 in a counterclockwise direction about pivot 29 to bring about a snap opening of contacts 26, 27.

As best seen in FIGURES 3 through 7, magnet 52 is is generally U-shaped member including web fill and arms 1 12, 162 extending forwardly from web 1M. Each of the arms 1% is stepped to provide a short portion 103 and a tall portion 1634- with short portion 193 being closer to armature pivot 53 than tall portion 194.

Armature 54 includes wide portion 1% and narrow portion 107 with wide portion 106 being closer to pivot 53 than narrow portion 107. The width of narrow portion 1&7 is slightly less than the spacing between tall portions 1114, 1114 while the width of wide portion 1% is greater than the spacing between narrow portions 1113, 103. For the structure illustrated, wide armature portion 1% is substantially the width of magnet web 161. The position of armature 54 and the length of wide portion 1% are such that when armature 54 is fully attracted to magnet 52 (FIGURE 5) narrow armature portion 107 will be disposed between tall portions 104, 1134 and wide portion 1% will rest uponpole faces 1113, 1% at the free ends of short portions 193, 163.

With current below a predetermined magnitude flowing through energizing conductor 32, armature 54 is in the latching positionshown in FIGURES 1 and With current exceeding this predetermined magnitude flowing through conductor 32 the flux generated by magnet 52 is sufiicient to overcome the biasing force of spring 51 thereby moving the narrow portion 1b? of armature 54 5 in a counterclockwise direction about pivot 53 to the trip position of FTGURE 5.

Tests have been conducted to compare a single turn magnetic structure having a stepped magnet 52 and cooperating armature 54 of the instant invention with conventional single turn magnetic structures in which the U-shaped magnet is not provided with a stepped portion and the armature is of uniform width throughout. Armature travel was the same for both magnetic structures. These tests show that for a given current magnitude flowing through the single energizing turn a greater force will be exerted on armature 5d of the instant invention than will be exerted upon the armature of the prior art device at the time when the armatures are in latching position. The force differential increases up to the point where narrow portion 107 is in position to move between tall portions 1%, 1% (FIGURE 4). Thereafter, the force differential decreases gradually until a point where narrow portion 187 is completely between tall portions 194, 104. For the remaining movement to the full trip position of FIGURE 5 the device of the instant invention does not exhibit any significant force advantage over the prior art device. However, once narrow portion 1W has reached the point in the opening stroke where it is about to move between tall portions 104, 104 the gap between pole faces 1%, 1618 and wide portion 106 has been reduced to such an extent that the pull on armature 54 far exceeds the biasing forces of spring 51 urging its latch tip 51a into latching position.

Thus, this invention provides a simplified construction wherein a single turn long stroke magnetic trip structure is provided which exhibits improved force characteristics when compared to similar devices of the prior art.

Although there has been described a preferred embodiment of this novel invention, manyvariations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appending claims.

clusive privilege or property is claimed are defined as follows:

1. A device of the'class described comprising a generally U-s'naped magnet having a web and arms extending forwardly from said Web, first means defining a pivot extending transverse to the planes in which said arms are disposed, an armature mounted at its first end to said pivot, second means biasing the second end of said armature to a position forward of said arms when said magnet is deene rgized, each of said arms having a short portion and a tall portion more remote from said pivot than said short portion, said armature having a wide portion and a narrow portion, said narrow portion being more remote from said pivot than said wide portion, said narrow portion being narrower than the distance between said tall portion, said wide portion being wider than the distance between said short portions, said armature having a first location corresponding to deenergization of said magnet and a second location corresponding to energization of said magnet; said armature when in said first location having its second end gap-separated from the forwardly extending pole faces of said tall portion; the forwardly extending pole faces of said short portion defining a plane; the extension of said plane towards said long portion more remote from said armature second end than said gap separation, whereby said tall portion effects a reduction in the armature gap-separation.

2; The device of claim '1 in which there is a single energizing turn for said magnet, said turn extending be tween said arms 1 V r The embodiments of the invention in which an ex- 3. The device of claim 1 in which the armature, upon energization of said magnet, is operable against the force of said second means to another position wherein said narrow portion is disposed between said tail portions.

4. The device of claim 3 in which said wide portion is disposed adjacent and parallel to the free ends of said short portions when said armature is in said another position.

5. A circuit breaker comprising a pair of cooperating contacts; an operating mechanism for opening and closing said contact, said mechanism including an operating spring and a releasable member which when released enables said spring to open said contacts; a latch means for maintaining said releasable member in a reset position; an automatic trip means comprising a generally U- shaped magnet having a web and arms extending forwardly from said web, first means defining a pivot extending transverse to the planes in which said arms are disposed, an armature mounted at its first end to said pivot, second means biasing the second end of said armature to a position forward of said arms when said maget is deenergized, each of said arms having a short portion and a tall portion more remote from said pivot than said short portion, said armature having a wide portion and a narrow portion, said narrow portion being more remote from said pivot than said wide portion, said narrow portion being narrower than the distance between said tall portions, said wide portion being wider than the distance between said short portions; means for energizing said magnet to operate said armature toward said magnet; an operative connection between said armature and said latch means whereby movement of said armature is effective to trip said latch means thereby bringing about opening of said contacts, said armature having a first location corresponding to deenergization of said magnet and a second location corresponding to energization of said magnet; said armature when in said first location having its second end gap-separated from the forwardly extending pole faces of said tall portion; the forwardly extending pole faces of said short portion defining a plane; the extension of said plane towards said long portion more remote from said armature second end than said gap separation, whereby said tall portion effects a reduction in the armature gap-separation.

6. The circuit breaker of claim 5 in which there is a single energizing turn for said magnet, said turn extending between said arms.

7. The circuit breaker of claim 6 also comprising a pair of terminals and current carrying elements comprising a series path between said terminals, said single energizing turn constituting one of said current carrying elements.

8. The circuit breaker or" claim 5 in which the armature, upon energization of said magnet, is operable against the force of said second means to another position wher in said narrow portion is disposed between said tall portions.

9. The circuit breaker of claim 8 in which said wide portion is disposed adjacent and parallel to the free ends of said short portions when said armature is in said another position.

It). A device, as set forth in claim 1, wherein said armature when in said second location is disposed in said plane defined by the pole faces of said short portion.

11. A circuit breaker as set forth in claim 5, wherein said armature when in said second location is disposed in said plane defined by the pole faces of said short portion.

12. A device of the class described comprising a generally U-shaped magnet member having a web and arms extending forwardly from said web, first means defining a pivot extending transverse to the planes in which said arms are disposed, an armature member mounted at its first end to said pivot, second means biasing the second end of said armature to a position forward of said arms when said magnet is deenergized; said armature when in its deenergized condition separated from the pole faces of said magnet by a substantially V-shaped gap, having a minimum dimension at the pivot, and progressively increasing in gap-separation towards said second end; one of said members having a portion at said second end extending into the V-shaped gap; said last-mentioned portion dimensioned to reduce the gap-separation at said second end, corresponding to said deenergizing condition, while permitting the armature when energized to close the V gap in the vicinity of said pivot end.

13. A device as set forth in claim 12, wherein said last-mentioned portion is a stepped portion of said arms, more forwardly extending from said web, than the arm portion adjacent said pivot end.

References Cited by the Examiner UNITED STATES PATENTS 2,089,716 8/37 Smith 200-109 2,328,458 8/43 Jackson et al. 20088 2,810,803 10/57 Green 200-88 BERNARD A. GILHEANY, Primary Examiner. ROBERT K. SCHAEFER, Examiner. 

12. A DEVICE OF THE CLASS DESCRIBED COMPRISING A GENERALLY U-SHAPED MAGNET MEMBER HAVING A WEB AND ARMS EXTENDING FORWARDLY FROM SAID WEB, FIRST MEANS DEFINING A PIVOT EXTENDING TRANSVERSE TO THE PLANES IN WHICH SAID ARMS ARE DISPOSED, AN ARMATURE MEMBER MOUNTED AT ITS FIRST END TO SAID PIVOT, SECOND MEANS BIASING THE SECOND END OF SAID ARMATURE TO A POSITION FORWARD OF SAID ARMS WHEN SAID MAGNET IS DEENERGIZED; SAID ARMATURE WHEN IN ITS DEENERGIZED CONDITION SEPARATED FROM THE POLE FACES OF SAID MAGNET BY A SUBSTANTIALLY V-SHAPED GAP, HAVING A MINIMUM DIMENSION AT THE PIVOT, AND PROGRESSIVELY INCREASING IN GAP-SEPARATION TOWARD SAID SECOND END; ONE OF SAID MEMBERS HAVING A PORTION AT SAID SECOND END EXTENDING INTO THE V-SHAPED GAP; SAID LAST-MENTIONED PORTION DIMENSION TO REDUCE THE GAP-SEPARATION AT SAID SECOND END, CORRESPONDING TO SAID DEENERGIZING CONDITION, WHILE PERMITTING THE ARMATURE WHEN ENERGIZED TO CLOSE THE V GAP IN THE VICINITY OF SAID PIVOT END. 